1,340 research outputs found
Searching for Imprints of Circumstellar Material in the Ultraviolet Spectra of Type Ia Supernovae
No full textType Ia supernovae (SNe Ia), having large and standard luminosities, are our primary dark energy probe. Although we believe that SNe Ia are produced by white dwarfs (WDs) in binary systems, the type of companion star is still unclear. Using a SN as a backlight, we can probe the gas along the line-of-sight to a SN Ia, including possible circumstellar gas from the companion star. For a handful of SNe Ia, repeated measurements of the narrow Na D doublet have shown variable absorption that we interpret as the recombination of circumstellar Na atoms after being ionized by the initial UV SN flash. This is perhaps the best evidence that at least some SNe Ia have a main-sequence or red-giant companion. Using Hubble Space Telescope ultraviolet spectroscopy, we probe several additional species with varying ionization potentials for 8 SNe Ia. Since these features have different ionization potentials from species seen in the optical, they probe new physical regions of the circumstellar system. Although these features can potentially reveal previously hidden circumstellar gas, we do not detect any variable features in our best examples, indicating that these systems had no circumstellar gas or that the gas was particularly distant.Submitted by Kayla Hays ([email protected]) on 2015-05-05T20:32:53Z
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Previous issue date: 2015-05Ope
Static-light hadrons on a dynamical anisotropic lattice
No full textJustin Foley, Alan O Cais, Mike Peardon, Sinead M. Ryan, Jon-Ivar Skulleru
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Improving Cosmological Utility of Type Ia Supernovae through Physics and Big Data
No full textAfter correcting for their light-curve shape and color, Type Ia supernovae (SNe Ia) are precise cosmological distance indicators. However, there remains a non-zero intrinsic scatter in the differences between measured distance and distances inferred from a cosmological model (i.e., Hubble residuals). We have found that Hubble residuals are correlated with different properties of SN Ia host galaxies (e.g., mass, star-formation rate, and metallicity). Cosmological analyses attempt to correct for these effects empirically without any physical knowledge of the progenitor system, potentially introducing a bias. In this thesis, I detail several projects aimed at uncovering the dominant physical sources of intrinsic scatter. First, I will present Kaepora, a relational database for SN Ia observations containing 4975 public spectra of 777 SNe Ia. We have significantly improved this data set by inspecting these spectra for quality, removing galactic emission lines and cosmic rays, generating variance spectra, and correcting for the reddening caused by both MW and host-galaxy dust. Using this large homogenized sample, we produce composite spectra that have been precisely controlled for phase and light-curve shape. These composite spectra reproduce known trends with other optical properties of SNe Ia, and by controlling for these effects, they can be used to investigate a wide parameter space. Critically, with these methods I will show that SN Ia distances can potentially be improved with the knowledge of their ejecta velocities. I will then describe late time observations of the UV-flashing high-velocity SN Ia 2019yvq. We identify strong Calcium emission in the nebular spectrum of this SN and argue that this indicates SN 2019yvq was likely the result of a sub-Chandrasekhar mass double-detonation explosion. It is possible that 2019yvq-like SNe contribute to our cosmological samples, and the presence of multiple progenitor channels could be a source of Hubble residual intrinsic scatter. A better understanding of SN Ia progenitor environments (which may correlate with progenitor channel) could help us discern the relative contributions of multiple progenitor channels in cosmological samples. Finally, I will present preliminary results from the Foundation/Swope host galaxy survey (a project which has spanned my entire graduate career). We have obtained optical spectroscopy for 372 out of 517 total SN host galaxies in the Foundation and Swope combined cosmological SN sample (the largest low-z sample). The mass-metallicity relationship of our preliminary sample is consistent with similar samples and contains some of the lowest mass galaxies studied in a cosmological sample. Our sample also shows evidence for a "metallicity-step" using measurements from both the galaxy nucleus and the supernova location. With the full sample, we hope to constrain the functional form of this relationship and better understand the underlying physical cause of the empirical host-galaxy correction
Re-dedication of Ryan Administration Building at Georgetown University
No full textThe building, erected in 1906 through the generosity of Mrs. Thomas Fortune Ryan, was remodeled in the early 1950s, at a cost of $200,000, to provide space for the offices of the Treasurer, University Records, Public Relations, Placement and University Development. Pictured at the re-dedication ceremony, left to right: Charles J. Foley, S.J., Director of University Development; Catherine Nolan, Executive Secretary of Georgetown Visitation Alumnae Association; Captain Parke Brady; Mrs. Parke Brady, granddaughter of Mrs. Thomas Fortune Ryan); and Anne McLaughlin, Director of University Record
Nonperturbative study of the action parameters for anisotropic-lattice quarks
No full textA quark action designed for highly anisotropic-lattice simulations is discussed. The mass-dependence of the parameters in the action is studied and the results are presented. Applications of this action in studies of heavy quark quantities are described and results are presented from simulations at an anisotropy of six, for a range of quark masses from strange to bottom.Justin Foley, Alan Ó Cais, Mike Peardon, and Sinéad M. Ryan (TrinLat Collaboration
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Unlocking Time-domain & Multimessenger Astrophysics and the Discovery of the First Optical Counterpart to a Gravitational Wave Source
No full textThe modern study of astrophysics is being transformed by advances across multiple fronts. New fast, wide, deep, and multi-color surveys are pushing into novel parameter spaces and generating an exponentially growing volume of data. Simultaneously, the first direct detection of gravitational waves (GWs) in 2015 has created a global race to search for their luminous counterparts. Here I present three major results that reside at the intersection of this new science and the methods, algorithms, and technology that enable it. The first is {\tt YSE-PZ}, a transient survey management platform that enables three major transient surveys: the Young Supernova Experiment, the Keck Infrared Transient Survey, and the Swope Supernova Survey. Second, I describe the discovery of the first optical counterpart to gravitational wave source, the kilonova (KN) SSS17a/AT 2017gfo. Discovering the KN and localizing it to the galaxy NGC~4993 paved the way for all the science that followed: it confirmed that there are electromagnetic (EM) counterparts to GWs, it allowed a redshift of NGC 4993 to be combined with the GW-derived luminosity distance to GW170817 and enabled the first standard siren measurement of H, and lead to the ability for rapid follow-up observations to confirm that binary neutron star (BNS) mergers are prolific astrophysical sites for the synthesis of the -process elements. Finally, I present a new ultraviolet, optical, and infrared search for the electromagnetic (EM) counterpart to GW190425, the second-ever BNS merger discovered by the LIGO-Virgo-KAGRA Collaboration (LVK). Intrinsic properties and observational limitations meant that any counterpart to GW190425 would be much harder to discover than SSS17a was, and neither our search, nor the broader EM community's search, discovered a credible counterpart. I contrast this speculative counterpart to SSS17a and discuss how KN diversity complicates our picture of heavy-element nucleosynthesis. I perform a combined analysis of the EM community's search for GW190425 using a new GW search and analysis tool called {\tt Teglon}. Through {\tt Teglon}, I calculate the most comprehensive upper limits on this potential EM counterpart to GW190425, as well as discuss opportunities for enhancing the community's coordination for the next BNS GW event in the LVK's fourth observing run and beyond
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Advancing Type Ia Supernova Science: The Swope Supernova Survey and Relationships Between i-Band Light Curve Diversity and Spectral Parameters
No full textSince the beginning of the modern telescope, astronomers have thought of new surveys and methods to study astrophysical phenomena. In this dissertation, I present the Swope Supernova Survey, a low-redshift photometric survey at Las Campanas Observatory, Chile, detailing its motivation, methodology, and significant contributions to transient astrophysics. I also highlight my vital contributions to the survey and science enabled. Since its inception in 2016, the survey has established itself as a critical resource for the study of transients below +30◦ declination, covering a wide wavelength range (u to i band), precise calibration, and high observing cadences. I specifically focus on the first Type Ia Supernova (SN Ia) data release, an effort that I led to provide over 100 high-cadence light curves in five photometric bands. This dataset enhances low-redshift SN Ia samples and opens the path for future work that will significantly contribute to SN cosmology. Finally, I introduce a novel parametrization of i-band light-curve diversity. I present the ∆m1 − ∆m2 parameter, which captures differences between the data and model at the i-band secondary maximum and minimum. Strong correlations are identified between this parameter and key spectral features, such as Ca II pEW0 and Si II v0, highlighting the role of spectral variations in shaping i-band light curves. This work also shows how these variations impact SN Ia composite spectra and synthetic photometry, revealing limitations in the widely used SALT3 SN Ia model. This dissertation highlights the importance of combining photometric and spectroscopic analyses to advance our understanding of SNe Ia, further exploring connections between SN Ia spectral features, i-band light-curve morphology and diversity, physical processes, environmental dependencies, and the accuracy of SNe Ia as precise cosmological distance indicators
Connecting people: Tackling exclusion? An examination of the impact on and use of the internet by socially excluded groups in London
No full textFoley lead author.
Foreword by Ken Livingstone, Mayor of London and response by Clive Ansell, Director BT, London.
Commisioned by: Greater London Authority, London Development Agency, LondonConnects and BThttp://static.london.gov.uk/gla/publications/e-london/connecting-commties.pd
The shadows of risk and inequality within salutogenic coastal waters
No full textThis is the author accepted manuscript. The final version is available from Routledge via the link in this recordEconomic and Social Research Council (ESRC
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